Cation/H+ antiporters mediate potassium and sodium fluxes in Pichia sorbitophila. Cloning of the PsNHA1 and PsNHA2 genes and expression in Saccharomyces cerevisiae

Pichia sorbitophila grows rapidly in the presence of very high NaCl concentrations. Under these conditions, even when the K(+) concentration is low, P. sorbitophila cells can maintain low Na(+) and high K(+) contents. This remarkable capacity of P. sorbitophila fails when the external pH is not acidic. This indicates that Na(+) efflux is mediated by an electroneutral Na(+)/H(+) antiporter. We have cloned and sequenced two genes designated as PsNHA1 and PsNHA2, which probably encode two antiporters of this type. The genes present high similarity with the corresponding genes from other yeasts. The heterologous expression of PsNHA1 or PsNHA2 in a Saccharomyces cerevisiae mutant lacking the Na(+) efflux systems and sensitive to high concentrations of Na(+) and K(+) rescued the tolerance and the ability to extrude both cations. The Accession Nos of the sequenced DNA fragments are: PsNHA1, AJ496431; PsNHA2, AJ496432. (TC 2.A.36) Copyright 2002 John Wiley & Sons, Ltd.     

Photobleaching of a solid photochromic medium by a Gaussian laser beam

Equations that describe the photobleaching of photochromic layers illuminated by Gaussian laser beams are given. The photochromic samples are made of thionine, triethanolamine, and polyvinyl alcohol and follow simple kinetics law. Spatial absorbance and time-dependent power transmittance are well described by the developed equations. The model is used to calculate the Gaussian dimension of helium-neon laser beams from kinetics data.     

New dendrimer-peptide host-guest complexes: towards dendrimers as peptide carriers

Adamantyl urea and adamantyl thiourea modified poly(propylene imine) dendrimers act as hosts for N-terminal tert-butoxycarbonyl (Boc)-protected peptides and form chloroform-soluble complexes. Investigations with NMR spectroscopy show that the peptide is bound to the dendrimer by ionic interactions between the dendrimer outer shell tertiary amines and the C-terminal carboxylic acid of the peptide, and also through host-urea to peptide-amide hydrogen bonding. The hydrogen-bonding nature of the peptide-dendrimer interactions was further confirmed by using Fourier transform IR spectroscopy, for which the NH- and CO-stretch signals of the peptide amide moieties shift towards lower wavenumbers upon complexation with the dendrimer. Spatial analysis of the complexes with NOESY spectroscopy generally shows close proximity of the N-terminal Boc group of the peptide to the peripheral adamantyl groups on the dendrimer host. The influence of side-chain motif on interactions with the host is analyzed by using seven different N-Boc-protected tripeptides as guests for the dendrimer. Downfield shifts of up to 1.3 ppm were observed for the guest amide NH-proton signals. These shifts decreased with increasing 'bulkiness' of the amino acid side chains. Despite this, the dendrimer was capable of making multiple peptide-dendrimer complexes when presented with a library of seven peptides. The different peptides were all present in the host, which did not show specific preferences, and could be released under mild acidic conditions. These results show the general nature of the peptide-dendrimer interactions in the formation of either single- or multiple-peptide-dendrimer complexes.     

An Auto-Adaptive Multidomain Spectral Technique for Linear Stability Analysis: Application to Viscous Compressible Flows

An auto-adaptive multidomain pseudo-spectral technique is considered in order to solve the linear stability problem of viscous compressible flows. Both the locations of the interfaces and the parameters of the mappings in each subdomain are adapted by minimizing the H ² -norm of the calculated solution. Such method provides automatically—this is the key point—the best polynomial interpolation of the basic state the stability of which is studied. It turns out that the whole procedure is needed to obtain reliable results. The method is first validated against results available in the literature (both viscous incompressible and inviscid compressible Rayleigh–Taylor configurations). The efficiency of the numerical method is illustrated with results on the linear stability of the compressible viscous diffusive Rayleigh–Taylor flow where no analytical or numerical results are available. New results showing the influence of stratification, viscosity, diffusity between species and thermal diffusivity are presented.     

Criteria for global minimum of sum of squares in nonlinear regression

Demidenko [2000. Is this the least squares estimate? Biometrika 87, 437-452] has established the relationship between the curvature of nonlinear regression and the local convexity of a sum of squares: the Hessian matrix is positive definite if the sum of squares is less than the minimum squared radius of the full curvature. In this paper, we continue developing the criteria for the global minimum of the sum of squares in nonlinear regression. In particular, the concept of the local unimodality is introduced; a function is called locally unimodal on a level set if it has a unique local minimum in each component of that level set. We show that the level of the local unimodality of the sum of squares is equal to the minimum squared radius of the intrinsic curvature of the nonlinear regression function. A new class of unidirected nonlinear regression models is introduced with an interpretation in terms of differential geometry. The criteria are illustrated by several popular nonlinear regression models.     

Development of an electromagnetic tool for the accurate synthesis of manifold multiplexers: The dynamic inverter

This article presents an electromagnetic tool for the synthesis of manifold multiplexers — the dynamic inverter. By associating this model with the classical circuit model of the filter, the broadband behaviour of each filter can be analysed rapidly and then optimised accurately for an efficient synthesis of the manifold multiplexer. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005.     

Electron Model of Solid Oxygen-Ionic Electrolytes Used in Gas Sensors

Yttria-stabilized zirconia (YSZ)-based ceramic gas sensors operating at high temperatures have been well established in many applications over the last 30 years. This article aims to provide an electron model of the solid electrolytes with oxygen-ionic conductivity used in gas sensors to simulate contact phenomena on the boundary of a YSZ/metal electrode interface within the solid-state zone theory. The primary focus of this article is modelling and assessment of the ability of a YSZ-based electrolyte to control oxygen potentials at low temperatures in different environments. The proposed model allows the necessary information with regard to the electrolyte/metal electrode interface and about the character of the electronic conductivity to be obtained. The model also describes that the character of the electronic conductivity in solid electrolytes usually depends on two mechanisms of charge transfer: electrons transfer in the conductivity zone, separated from the valent zone in the solid electrolyte by the wide enough forbidden zone, and the spasmodic transitions of electrons from one local level to another within the forbidden zone.     

Spontaneous Desorption time-of-flight Mass Spectrometry (SDMS): Time correlated emission of electrons and negative ions in a constant electric field

A very simple time of flight mass spectrometer has been used to measure mass spectra for the negative ions of organic compounds in the mass range up to 3000 u. Desorbed ions were obtained by applying a constant negative voltage to a flat metallic surface, coated with a few micrograms of organic material. We show that electrons and negative ions are emitted simultaneously from the same point on the surface. Mass spectra obtained by this technique are compared to mass spectra for the same compounds, obtained with ²⁵²Cf fission fragment ionization.     

Normalized cuts in 3-D for spinal MRI segmentation

Segmentation of medical images has become an indispensable process to perform quantitative analysis of images of human organs and their functions. Normalized Cuts (NCut) is a spectral graph theoretic method that readily admits combinations of different features for image segmentation. The computational demand imposed by NCut has been successfully alleviated with the Nystr?m approximation method for applications different than medical imaging. In this paper we discuss the application of NCut with the Nystr?m approximation method to segment vertebral bodies from sagittal T1-weighted magnetic resonance images of the spine. The magnetic resonance images were preprocessed by the anisotropic diffusion algorithm, and three-dimensional local histograms of brightness was chosen as the segmentation feature. Results of the segmentation as well as limitations and challenges in this area are presented.